Graft copolymers of nitrile groups on polyamide substrates



United States Patent 3,413,378 GRAFT COPOLYMERS OF NITRILE GROUPS ONPOLYAMIDE SUBSTRATES Eugene Edward Magat, Spring Valley, Wilmington,Del., and David Tanner, Charlottesville, Va., assignors to E. I. du Pontde Nemours and Company, Wilmington, Del., a corporation of Delaware NoDrawing. Continuation-impart of application Ser. No.

578,414, Sept. 9, 1966, which is a continuation of application Ser. No.863,047, Dec. 30, 1959. This application Nov. 14, 1966, Ser. No. 593,659

6 Claims. (Cl. 260-857) ABSTRACT OF THE DISCLOSURE Shaped structures ofa graft copolymer comprising a polyamide and side chains bearing nitrileradicals, grafted thereto, by carbon to carbon bonds. Structures haveimproved light durability, resistance to soiling, crease recovery,dyeability, and resistance to caustic attack and wrinkling, as comparedto unmodified polymer.

This application is a continuation-in-part of application Ser. No.578,414, filed Sept. 9, 1966, which is a continuation of applicationSer. No. 863,047, filed Dec. 30, 1959 (now abandoned), which is adivision of application Ser. No. 735,288, filed May 14, 1958, now U.S.Patent 3,188, 228, which is a continuation-in-part of our abandonedapplications Ser. No. 499,754, filed Apr. 6, 1955, and Ser. No. 503,790,filed Apr. 25, 1955.

INTRODUCTION This invention is concerned with fibers from graftedsynthetic polymeric esters and amides.

STATE OF THE ART Grafted copolymers have been developed for manyenduses. Grafted synthetic linear condensation polymers have beenstudied less extensively than the addition polymers, since the latterare especially adapted to grafting reactions requiring free radicalactivity, which may be present as a result of the polymerizationprocess, or may be induced by activating residual unsaturated (double)bonds.

By means of these grafts, properties not normally found in condensationpolymers may be provided. For example, increased reactivity, improvedstatic resistance, resistance to hole melting and the like can beattained without significant loss in the properties of the substratepolymer.

OBJECT It is an object of the present invention to provide a graftcopolymer of a polyamide or polyester substrate which has improvedresistance to soiling, caustic attack and wrinkling, improved lightdurability, crease recovery, and dyeability, as compared to unmodifiedpolymer.

THE INVENTION These and other objects are attained in a graft copolymertextile comprising (a) a synthetic linear condensation polymer substrateselected from the class consisting of polyamides and polyesters, and (b)side chains bearing nitrile radicals, grafted thereto, by carbon tocarbon bonds.

The polyamide which serves as a substrate for grafting is afiber-forming polyamide wherein the amide linkage is an integral part ofthe polyamide chain. Similarly, the polyesters are those wherein theester linkage is an integral part of the polymer chain. The graftedpolymer chains are bonded by carbon-carbon linkages to the substratepolymer backbone.

The preferred modifier for grafting to the condensation polymersubstrate is acrylonitrile. However, other unsat- Patented Nov. 26, 1968urated nitriles are useful, such as the OL-SubStitllted nitriles,for-example, methacrylonitrile, the cyano substituted styrenes,dinitriles such as vinylidene dinitrile and the like.

Although useful modifications are obtained when as little as 1%acrylonitrile is grafted to the substrate, it is desirable to graft from4 to by weight; the preferred range is from 10 to 50% weight increasefor polyamides.

Grafting is most conveniently initiated by high energy radiation, suchas high energy electrons, X- or gammarays. The polymer substrate may besoaked in the modifier either as a liquid or as a solution and thecombination irradiated in a single step operation. Alternatively, thepolymer substrate may be irradiated at room temperature and thenpreferably substantially immediately, contacted with the modifier in atwo-step process. A preferred embodiment of the two-step process is toirradiate the polymer below 10 C., preferably below 0 C. and thencontact it with the modifier. Grafting occurs as the combination iswarmed.

The invention is illustrated by the following examples but it is notlimited thereby. Unless otherwise indicated, weight percentages areintended. Irradiation doses are given in mrad where l mrad is equal to1,000,000 rads.

Example 1 A sample of 66 nylon (polyhexamethylene adipamide) fabric isimmersed in liquid acrylonitrile. It is then wrapped in aluminum foiland irradiated with 2 mev. X-rays, as described below, until a dose of23 mrads is attained.

The sample is exposed to X-radiation using a resonant transformer X-raymachine marketed by the General Electric Co., Schenectady, N.Y., knownas a Two Million Volt Mobile X-ray Unit. This machine is described by E.E. Charlton and W. F. Westendorf in the Proceedings of the FirstNational Electronics Conference, p. 425, October 1944, The packagedsample is placed in an open top box made from A inch sheet lead, andpositioned so that the sample is 8 cm. from the tungsten tube target. Atthis location, using a tube voltage of 2 mev., and a tube current of 1.5milliamperes, the irradiation rate for the sample in question is 1.2mrads per hour. The beam irradiates a circle about 3 inches in diameter;all fabric tests are made on the irradiated portion.

Following the irradiation, ungrafted polymer is removed by washing withdimethylformamide. After 15 hot water washings in a household detergent,the dried nylon fabric has a superior crease recovery and greaterresilience than before treatment by the process of this invention.

A second sample is immersed in liquid acrylonitrile. It is then wrappedin aluminum foil and irradiated as before to a dose of 5 mrads. Afterthorough rinsing, the weight gain is 12%. Larger irradiation dosesproduce larger weight gains.

It is shown that a bulk modification has been obtained by hydrolyzingthe nylon-acrylonitrile graft by a 30 minute boil-off in 3% sodiumhydroxide. The fabric which now contains a large number of additionalcarboxyl groups due to hydrolysis of the nitrile groups, is then dyedwith a basic dye (Cl. No. 662). Cross-sections of filaments taken fromthese fabrics are deeply dyed throughout the modified filament, whereasonly light shades are observed in cross-sections of filaments taken fromcontrol fabrics which had received the same caustic boil-off and dyeingtreatment without irradiation. The hydrolyzed test fabric has a log R of9.4 vs. 13.3 for control, showing decreased tendency to accumulatestatic charges (see A.A.T.C.C. Test Method 76-1959).

Example 2 A sample coded A of 66 nylon fabric is immersed in liquidacrylonitrile. It is then wrapped in aluminium foil and irradiated withone million electron volt (l mev.) electrons using a resonanttransformer with a beam-out current of 560 microamperes. The sample istraversed back and forth under the beam until a dose of 17 mrads isattained. The product softens at 240 C. and is almost completely solublein formic acid. It is observed to possess a higher crease resistance andgreater resiliency than the original sample. This improved resiliency isretained even after 15 washings in a household detergent following awashing in dimethylformamide (a solvent for polyacrylonitrile).

The test is repeated with 66 nylon samples C and D, which are soaked 24hrs. at 25 C. in solutions of acrylonitrile, water and methanol, asindicated in Table 1. Each sample is enclosed in a polyethylene bag withexcess solution and .is irradiated using a 2 mev. Van de Graff electronaccelerator with a beam-out current of 250 microamperes. The samples aretraversed twice under the beam to give a dose of 2 mrad.

After a hold-up time of 2 hours, the samples are thoroughly rinsed indimethylformamide at 70 0, followed by acetone and then water. Theweight gain of each is determined and listed in Table 1. The breakingstrength of representative yarn samples from each fabric is determinedafter and 500 hours exposure to ultraviolet light in a Weatherometer. Acontrol, B, is included in the table for comparison purposes; thecontrol is not exposed to the high energy electrons.

*Solution composition=ml. acrylonitrile/ml. H2O/1I1l. CHsOH.

The grafted acrylonitrile greatly increases the light durability of thenylon.

Example 3 A series of sample swatches of tropical worsted staple fabricprepared from polyethylene terephthalate filaments are soaked in a 50%solution of acrylonitrile dissolved in a mixed solvent of 42% ethanoland 58% water, and are then heated at 90 C. for 30 minutes. The fabricsamples are transferred to stainless steel pans containing 200 ml. ofthe treating solution, and irradiated for one pass (dose, 1 mrad) undera 2 mev. electron beam at 250 microamps. The irradiation temperature is90 C. The grafted fabric is extracted in boiling dimethylformamide toremove unreacted monomer and unattached polymer, after which it is driedat 80 C. The observed weight gain is 4.4%. The test is repeated, withfabric samples A, B and C. The composition of treating solutions,radiation dose and weight gain are shown in Table 2.

The acrylonitrile-grafted polyethylene terephthalate is found to be moreresistant to alkaline hydrolysis (e.g., resistant to scouring) than theungrafted fabric; it is also more resistant to soil pickup. Fabricssamples A to D, in which D is a control bearing no graftedacrylonitrile, are subjected to a laboratory test for laundry soiling.In this test fifty 4 inch steel balls, 0.1 g. of vacuum cleaner soil,0.04 g. carbon black, and 20 ml. of Wagg oil, (R. E. Wagg: J. Text.Inst., 1952, T5l5.), are placed in a pint Launder-Meter jar. Afterevaporation of the oil vehicle, 100 ml. of 0.1% soap solution(commercial laundry soap) is added. This mixture is then conditioned(with occasional stirring) for 1 hour at 72 C. Two 3" x 3" fabricswatches (test-l-cotton control) are placed in each jar, and the mixtureis tumbled for 1 hour. The swatches are then removed, rinsed thoroughly,and allowed to dry. Each swatch is then pressed for 30 seconds at l60170C. using a hand iron. Refiectances are measured before and after washingand after pressing. At least 3 samples Cir of each fabric are used (3jars), and the refiectances averaged. Results are recorded either asdifferential in re fiectance (DR) between original sample and washedsample, or differential between original sample and ironed sample. Thedifference in reflectance of the samples is determined before and afterthe laundry test and is indicated in the column headed DR of Table 2. Alow value for DR indicates nearly complete removal of soil, whereas ahigh value for DR indicates a fabric which retained all the appliedsoil. Cotton normally gives a DR value of 7 to 9, which is consideredsatisfactory. It is observed that soil removal improves with the amountof acrylonitrile grafted. In addition, the grafted polyethyleneterephthalate fabric is more resistant to an alkaline hydrolysis. Thisis shown in the last column of Table 2, wherein the ratio of weight lossfor the test item to that of control (D) is indicated for a two-hourboil in 1% sodium hydroxide solution. Again, increased amounts ofgrafted acrylonitrile show increased alkaline stability. When the testis repeated using (a) a mixture of acrylonitrile and a-methyl-styrene or(b) acrylonitrile and styrene, resistance to alkaline hydrolysis isimproved over that obtained when only acrylonitrile is grafted.

TABLE 2.ANTISOILING AND ALKALINE SENSITIVITY OF POLYETHYLENETEREPHTHALATE Sample Treat solu., Percent Dose, D. R. Alkaline N0.percent AN* wt. gain mrad sensitivity 20 1 12 0.84 2.4 2 11 0. 74 4.4 18 0. 71 None 17-20 1. 00

*AN =acrylonitrile in ethanol-water solvent.

A portion of sample C is dyed for 2 hours at the boil with a dispersedye, in a bath containing 0.13 gm./l. C.I. No. Disp. Red 11, 1.0 g./l.of an anionic hydrocarbon-sodium-sulfonate softener, 2.5 g./l. dimethylterephthalate, 2.5 g./l. benzamide. A bath-to-fabric ratio of 40:1 isemployed. The dye is exhausted, and scoured sample C is found to have adeep, attractive shade. Control D, similarly dyed, does not exhaust thebath, and the shade is much lighter.

A second portion of C is dyed, using the cuprous ion technique, asfollows: the sample is placed in a bath (bath-to-fabric ratio, 40:1) at72 C. containing (based on weight of fabric) 1% Cl. No. Acid Yellow 2,0.1% sodium salt of unsaturated long-chain alcohol sulfate (wettingagent); the temperature is raised to 82 C., and 2.5% copper sulfate isadded, followed by 1.0% hydroxyl ammonium sulfate; the bath is thenheated to the boil for 2 hrs., followed by a scour. Test sample C isdyed a good shade, whereas in an attempt to similarly dye the control,D, it remains uncolored.

METHOD OF APPLICATION The substrate polymer may be contacted with themodifier composition before or after irradiation, as already stated. Itmay be applied to the fiber as a liquid or vapor, or may be applied as asolution or an emulsion. Some peneration of the composition into thepolymer is usually desirable; chosing a solvent having a swelling effecton the substrate will increase the rate of diffusion. Presoaking in themodifier solution before irradiating will also enhance penetration.Alternatively, the polymer may be preswollen with swelling agent beforecontacting with the modifier composition. When contacting preirradiatedsubstrate polymer, it is usually helpful to heat the modifiercomposition containing the preirradiated substrate to accelerate thereaction. This is especially helpful with polyethylene terephthalate,which grafts best at temperatures above C. In general, however,temperatures of 50 to C. are satisfactory.

It is within the scope of this invention to employ multifunctionalunsaturated modifiers to produce some addi tional effect such asimproved antistatic effect, flame resistance, hand, and the like, aslong as the modifiers also contain nitrile radicals. It is preferredthat no more than 49% of any other graft component be present.

IRRADIATION CONDITIONS By ionizing radiation is meant radiation havingsufficient energy to remove an electron from a gas atom, forming an ionpair; this requires an energy of about 32 electron volts (ev.) for eachion pair formed. This radiation has sufficient energy to non-selectivelybreak chemical bonds; thus, in round numbers radiation with energy of 50electrons volts (ev.) and above is effective for the process of thisinvention, although energies of 50,000 ev. and over are preferred. Bothparticle radiation and ionizing electromagnetic radiation are included.

The preferred radiation for the practice of this invention is highenergy ionizing particle radiation; for maximum utility, when using thistype of radiation, energy equivalent to at least 0.1 million electronvolts (mev.) is preferred. Higher energies are even more effective;there is no known upper limit, except that imposed by availableequipment.

The high energy particle radiation is an emission of highly acceleratedelectrons or nuclear particles such as protons, neutrons, alphaparticles, deuterons, beta particles, or the like, directed so that thesaid particle impinges upon the polymer.

Similarly, ionizing electromagnetic radiation (X-rays) useful in theprocess of this invention is produced when a metal target (e.g., gold ortungsten) is bombarded by electrons possessing appropriate energy, e.g.,0.1 mev. In addition to X-rays produced as indicated above, ionizingelectromagnetic radiation suitable for carrying out the process of theinvention may be obtained from a nuclear reactor (pile) or from naturalor artificial radioactive material, for example, cobalt 60.

The dose rate (intensity of dose) is not critical, being primarily amatter of available equipment. In general, high dose rates are preferredas promoting higher throughput.

Efiiciency of dose utilization will usually be improved by keeping thefiber and excess monomer mixture in contact for an extended time afterirradiation, with either the two-step on one-step process. This willprovide maximum opportunity for the radical-initiated chains to grow.

SUBSTRATE SHAPE The product of the instant invention may be graftedbefore or after converting to its final (i.e., filament) shape, if themodifier is sufficiently stable thermally to stand the temperaturesrequired for melt spinning. It is preferred to graft to the fiber. Whenthe fiber is grafted, it may be grafted before or after drawing. It maybe grafted as yarn, staple, flock, tow or fabric of knitted, felted, orwoven construction.

SUBSTRATES Substrates useful for the graft copolymer of this inventionare the synthetic linear fiber-forming polyamides and polyesters. Thepolyamides are characterized by recurring amido radicals as an integralpart of the polymer chain. The amido radicals are linked by divalentorganic radicals which may be aliphatic, cycloaliphatic or aromatic, ormixtures of the above. Typical polyamides are poly(hexamethyleneadipamide), polycaprolactam, poly- (hexamethylene sebacamide),polyaminoundecanoamide, poly(hexamethylene isophthalamide),poly(2-methyl hexamethylene terephthalamide), poly(metaxylyleneadipamide), poly(para-xylylene sebacamide), poly(octamethyleneoxalamide), and the polyamide from his (4- aminocyclohexyl)methane andaliphatic acids such as dodecanedioic acid. Copolymers having two ormore components, as well as polymer and copolymer mixtures of the aboveare also included.

In addition to the polyamides, the invention is especially applicable tothe crystallizable, linear condensation polyesters. These compriselinear polyesters containing in the polymer carbonyloxy linkingradicals,

O in) Polymers containing oxycarbonyloxy radicals are comprehended withthis group. The polymers should be of fiberforming molecular weight;usually, this implies a relative viscosity of about 10 or higher asconventionally measured in solution in a solvent for the polymers. Agood solvent for most of the linear condensation polyesters is a mixtureof 58.8 parts phenol and 41.2 parts of trichlorophenol. Copolyesters,terpolyesters, and the like are intended to be comprehened within theterm polyesters.

Examples of crystallizable, linear condensation polyesters includepolyethylene terephthalate, polyethyene terephthalate/isophthalate(85/15), polyethylene terephthalate/S-(sodium sulfo)isophthalate (97/3),poly(phexahydroxylylene terephthalate), polyhydroxypivalic acid,poly(decahydronaphthalene-2,6-dimethylene 4,4-bi benzoate), polyethylene2,6- or 2,7-naphthalenedicarboxylate, andpoly(bicyclohexyl-4,4'-dimethylene-4,4-bibenzoate), as well as manyothers. Preferably, the polyester is a linear glycol terephthalatepolyester. By this is meant a linear condensation polyester derived froma glycol and an organic acid in which the glycol component is comprisedsubstantially of a dihydroxy compound of a divalent saturatedhydrocarbon radical containing from 2 to 10 carbon atoms and the acidcomponent is at least about mol percent terephthalic acid.

UTILITY The graft copolymers bearing nitrile radicals according to thisinvention have improved light durability, resistance to soiling, static,and alkaline hydrolysis. Partial hydrolysis of the acrylonitrile graftedto polyethylene terephthalate results in fibers and fabrics that aremore readily dyeable especially with basic dyes; the polymer substrateis also protected against hydrolytic degradation. Improvement inwickability and comfort is also noted.

What is claimed is:

1. A shaped structure of a graft copolymer formed from a polyamidewherein the recurring amide linkages are an integral part of the polymerchain, the shaped structure of the said polyamide having side chainsbearing nitrile radicals graft polymerized thereto.

2. The structure of claim 1 in the form of a filament.

3. The structure of claim 1 in the form of a film.

4. The structure of claim 1 wherein said side chains arepoly(acrylonitrile) 5. The structure of claim 4 wherein said polymer ispolyethylene adipamide.

6. The structure of claim 1 wherein said polymer is polyhexamethyleneadipamide.

References Cited UNITED STATES PATENTS 3,115,418 12/1963 Magat 204159.l5

FOREIGN PATENTS 679,562 9/1952 Great Britain.

MURRAY TILLMAN, Primary Examiner. P. LIEBERMAN, Assistant Examiner.

